Telephone or like system



Feb. 6, 1945. R. TAYLOR ET AL 2,369,086

I TELEPHONE OR LIKE SYSTEM Filed Jan. 12, 1942 3 Sheets-Sheet l IIIIHIILI llllllllll IN VEN TORS REGINALD TAYLE R GEORGE THOMAS BA KER ATTORNEY Feb. 6, 1945. R. TAYLOR ET AL v 2,369,086

TELEPHONE OR LIKE SYSTEM I Filed Jan. 12, 1942 3 Sheets-Sheet 2 u.- 12g .R. u/s

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TELEPHONE OR LIKE SYSTEM Filed Jan. 12, 1942 3 Sheets-Sheet 5 INVENTERS REGINALD TAYLOR GEORGE THOMAS BAKER ATTORNEY Patented Feb. 6, 1945 UNITED STATES PATENT OFFICE TELEPHONE on LIKE SYSTEM '1 Claims.

The present invention relates to telephone and like light current signalling and/or control systems having facilities for speech communication, and it has for its general object the provision of an improved method of signalling over speech communication circuits, which signalling method will not interfere with conversations which may be already in progress on said circuits and which is substantially immune from interference either by the speech currents or by other currents and voltages which may occur thereon.

According to the invention signals are transmitted over line wires of a signalling system after a conversational circuit has been completed thereover, which signals take the form of pulses having a rhythm or cadence below the audible range, which pulses are of such form as to have no or substantially no harmonics in the speech frequency range of a nature such as to be audible to those using the conversational circuit. Differs ent signals are characterised bypulsesof different rhythms -1 by combinations of pulses of dif: ferent rhythms. x a

Other features of the invention concern the arrangements for applying such signals to a conversational circuit,.for instanceJby superimposing them upon an existing'direct current circuit and the application of such signalling arrange-g ments in a telephone system such as to enable,

multi-fee determining arrangements forapluconnection whichar'e necessary for the purpose,

ofeffecting multi-metering against a calling satellite exchange subscriber.

.Referringnow to Fig. 1, the inner circle represents the central automatic area which is usual- 1y of five miles radius and which embraces a number of exchanges comprising a main exchange M and satellite exchanges A, B and C thereon,

all of which are, brought into onelinked numbering, scheme. It is assumed that aunit meter feel is "chargeableffo'r all calls set up and comcally but inwhichjthe' number of. meter registr'ations will vary in accordance with the exchange involved. The outlyingv exchanges with- .in this multi fee area but outside the central rality of exchanges to be located at a's'elected exchange and. signals of different kinds corre-j sponding to the difierent fees to be transmitted to the originating exchange to efiect the appro# priate operation of the calling subscribers meter.

The inventionwill be better appreciated from the following description of one example of its application, reference being had to the accompanying drawings comprising Figs. 1 to 4 in which the invention is' shown as regards its application for centralising at a main exchange the multifee metering facilities for main and satellite exchanges innon-register translator telephone ex: change areas. v

A layout of a typical area of this type is shown in simple form in Fig. 1, while Fig.2 showsa trunking diagram of the essential apparatus involved in setting up either a single-fee call from satellite exchange A to the'main exchange M or a call from exchange A and through the main exchange M to an outlying exchange within the area, the connection to which may require multifee meter registration. Figs. 3 and 4 when arranged side by side with Fig. 3 on the left, show the circuits of that part of the lattertype of linked numbering area, are designated 'a e.

A subscriber on satellite exchange A on setting up a call to any of the exchanges within the central area will only becharged an ordinary. unit fee registration, but in case a call is being setup to any of the exchanges a, b, c, d or e which call will also be routed via the main exchange M,- then it is necessary to charge one or. more unit f ees in accordance with the particular exchange being called. v

' For this purpose it has already been proposed that the first selectors at a satellite exchange such as. A shall be comparable to an ordinary first numerical selector and shall, on seizure, gain access to one of a common group of so-called discriminating and multi me'tering equipments which in addition to performing the functions normally provided in a discriminating selector repeat er, serve also to determine the appropriate meter fee in accordance 'with the first one or more of the digits of the dialled number.

' The amount of apparatus required' for multimetering purposes is quite a considerable item,

since the meter fee required cannot'be determined until all the'route-determining digits have been dialled, which may comprise one, two or more digits. In the case of small satellite exchanges it will be further appreciated that the common discriminating and multi-metering' equipments will be worked quite inefliciently owing to the small groups involved and the total amount of equipment required per exchange for multi-metering may form an unduly high proportion of the total exchange equipment.

It is therefore proposed according to a feature of the invention by providing suitable signalling means for transmitting signals over a conver- I all cases.

sational circuit that the various satellite exchange multi-metering equipments should be combined in a common group at the main exduced for the same traflic carrying capacity.

The signalling scheme already generally described lends itself readily to this purpose.

1-7 and 9 which indicate that a subscriber in the central linked numbering area is required, for which a unit meter fee is chargeable, selector repeater DSR after stepping in parallel with the incoming. selector ISR in response to the first digit will release the juncticninthe case of a calllocal to exchangeA a'ndponnect up with a local second selector, or will retain the junction connection and will repeat subsequent digits It may be mentioned here that the various Y outlying exchanges a,e, which are outside the 1 central area but within the [multi-fee dialling area, will not usually be brought into the centralised multi-metering scheme, as they will often I be of the rural automatic exchange type. the

design of which includes facilities for multi-' metering and like discriminations. The application of the invention to be described is therefore concernedonly with the centralisation of 1 meter fee determining facilities for groups of satellite exchanges dependent on a main change. V

Returning to the consideration of Fig. 1 it ,will

be arranged that where a subscriber on an exchange such as A wishes to gain access to another subscriber on any of the exchanges within the unit fee linked numbering area, the directory number will be dialled, which number may commence with any digit except digit 8. Forcalls requiring to be extended outside the central area but inside the multi-fee area, then a two or three 1 digit code will be prefixed to the called sub-' scriber's number, the first prefix digit being 8 in All outgoing calls from the satellite exchanges A, B and C must be set up via the dialled over the junction to the incoming selector ISR and outlets such as 12 to switches convnecting with the required subscriber either on rangements are made for access to be obtained to the main. exchange manual board either over the ordinary junction l0, II or in other manners, in

which the present invention is-not concerned.

If the first digit dialled is 8 the satellite DSR after having been stepped up to level 8 in par-- allel with theincoming selector ISR will retain the junction connection and will repeat'subsequent dialled digits. It will be seen that access is had 'from'level 8 of the selector ISR to an outgoing ijunction set OJS which has directly associated therewith an outgoing selector'OGS and which on seizure is adapted to associate itself with an idle one of a common group of route discriminating equipments such as RDEvia a hunting switch U/S2. Provided in the outgoing relay set is an impulse storage and regenerating device for instance of the electromechanical type disclosed in Patent No. 2,188,461

main exchange M and to ensure that the number i of digits to be dialled to set up a connection will never exceed a predetermined maximum irrespecti've of the number of switching stages en route, it is arranged that the dialling of the first digit 8 will enable'a type of register-translator equipment, knownas a route discriminator, to be. taken into .use and this will respond to two succeeding dialled digits to effect a'translation f to route the call to the required exchange. This equipment is also adapted, in response to the 1 digits which it receives, togdetermine the. required meter fee and on the reply of the called party thisv is subsequently signalled back to the calling partys meter in a manner to bellater described.

Referring now to the trunkingdiagram of Fig.

2, since it is to be arranged according to the invention that multimetering equipment is not to 3 be provided in the satellite exchanges such as A but to be available in a common pool at the main exchange, then this satellite exchange may be provided with discriminating selector repeaters to receive the first digit instead of having common groups of dscriminating equipment to which access is had from first numerical selector switches on origination of a call. When a subscriber at exchange A removes the receiver of his telephone instrument T a line finder LF. of the two-motion vertical and rotary type, is

granted January 30, 1940, and assuming that the called number comprises the initial'digit 8 fol-' lowed by two further code prefix digits and the subscribers number then it will be understood that the second and third digits dialled, i. ethe code 'ligits which serve to determine the rout-- ing, will be received. on the impulse storage and regenerating device in the relay set OJ Sand will be immediately retransmitted therefrom into the route discriminator equipment RDE. The two digits received by thediscriminator position a 2- motion switch therein to determine the required translation and also-to enable the required meter fee to be determined, After reception'of these two digits a signal issent back to relay set OJS to prevent the impulse storage and regenerative device from sending out-any further digits received. The necessary grouting digits are now transmitted from the discriminator and these extend via the relay set OJS, theout oing switch OGS and subsequent'swit'ches atthe main and other intermediate exchanges, if any, to the required exchange, it being appreciatedthat during this time the reception of theremaining digits of the dialled number on theimpulse storage and regenerating device may also be taking place. After all the routing digits have been transmitted from the discriminator asignal is sent forward to the outgoing'relay set to, release. the dialled digits stored therein, whereupon these are re-transmitted in untranslated form to complete the setting of the connection.

Discriminator RDE after having determined the meter fee communicates this information to a pair of relays in the main exchange first selector ISR While after it has completed the sending out of the routing digits it drops out .of the connection. Subsequently, when the called subscriber answers, signals are transmitted from selector ISB to the calling satellite exchange over the conversational path in order to register the required meter fee in a'manner which will be apparent from the following description of the circuit diagram of Figs. 3 and 4.

Referring now to these figures, it will be seen that a calling telephone instrument T isconnected via line finder LF, discriminating selector repeater DSR and hunting switch U/S at satellite exchange A to the main exchange incoming selector ISR over the junction line H], H and it will be understood that the wipers of this latter switch gain access over level 8 to an outgoing junction relay set as described in connection with Fig. 2.

In the present example of carrying the invention into efiect it is assumed that on reply of the called party the first meter registration, irrespective of whether the connection is single or multi-fee, is eifected in usual manner by means of a battery reversal extended backwardly over the speaking leads to the satellite DSR.

In the case of a call which is being routed out over level 8 of the main exchange selector ISR a meter fee of more than one unit may be required.

In the present example it will be assumed that a maximum of 4 may be required. The route discriminator serves to determine whether any metering units additional to the one already described are required and it communicates this information to relays MMA and MMB (Fig. 4) of the selector ISR. If relay MMA is alone operated it will be understood that one additional metering pulse will be transmitted to the calling satellite exchange; if relay MMB is alone operated two additional pulses will be transmitted, while if both relays MMA and MMB are operated, three pulses will be transmitted. If the call is to be a.

single fee call even though it is extending outside the central area then neither of the relays MMA nor MMB will be operatedand no metering pulses additional to the original one will be transmitted.

Considering now the circuit operations of Figs, 3 and 4, when the called party replies thefeeding battery at the distant exchange is reversed in usual manner, whereupon relay DM (Fig. 4) which is normally shunted by rectifier MRC in a conducting direction and which is connected across the line via the winding of retard IM and armature 111122 of the operated impulsing and battery feeding relay AM, now operates. A start circuit is thereupon completed via armature dmI to the well-known S and Z pulse operated DA and DB relay combination, while at the same time at armatures dm3 and dml the feeding battery to the calling satellite exchange is reversed. Relay D thereat (Fig. 3), which is polarised by the parallel 1 connected rectifier MR-B, now operates, relays RA and RB being inoperative since they are of special type, and in well-known manner (not shown) causes a pulse of positive battery to be returned over the incoming P lead so as to produce one registration of the calling subscribers meter MTR. This meter has connected in circuit therewith a rectifier MRE which prevents it from re sponding to anything except positive battery signals.

If any further registrations require to be made on the subscribers meter M'I'R as signalled to selector ISR by the operation of either or both of the relays MMA or MMB, this selector prepares for the sending out of the necessary signals to'the satellite DSR and these signals will have to be sent out over the speaking leads at a time when conversation .may be taking place between the calling and called parties without causing interference with said convensation.'v

The signals as previously stated comprise trains of rhythmic pulses at a low non-audible frequency preferably of the order of 1-2 cycles per second which will be supplied to the speaking conductors of the line from a direct current positive battery source, the pulsing circuit being suitably smoothed to prevent interference with conversation by eliminating audible frequencies. One, two or three meter pulses will have to be signalled by this method and it is proposed to employ two difierent rhythm frequencies which will be received at the satellite DSR on rhythm responding movements RA and RB respectively, for instance, of a mechanical construction similar to that disclosed in British Patent No. 518,877, issued March 11, 1940 to John Francis Mackenzie and comprising a slow beat type movement in the form of an oscillatory system controlled by a spiral spring, the size and adjustment of which determines the particular low rhythm frequency to which the device is to respond. These responding movements are tuned respectively to the two different rhythm signalling frequencies involved and they are placed in series with the ordinary D and I relays of the DSR and their operation either singly or in combination energises relays to provide the requisite number of additional pulses required to make up the total necessary meter fee.

Returning again to the main exchange selector ISR, relay BM in operating connects relay DA at armature rim] to the S pulse lead of a delay period timing set extending from so-called S and Z pulse cams (not shown) arranged to supply battery pulses with a definite timed relationship to two correspondingly marked leads as shown in graphical form at the foot of Fig. 4. On transmission of the next 5 pulse which indicates the beginning of a complete cycle of operation relay DA is operated on its upper winding, locks over its intermediate winding to earth via armatures dmZ, 11b2, dal, cm2 and bml and prepares a circuit for relay DB which is operated after the appropriate time interval from the Z pulse in series with the lower winding of relay DA. Relay DB in operating at armatures db3 and dbZ cuts off the initial operating and locking circuits for relay DA and at conclusion of the Z pulse relay DA restores and relay DB remains locked on its lower winding via armatures dbl, cm2 and bml to earth to prevent re-operation of relay DA from a succeeding 8 pulse and therefore to prevent a repetition of the signal train which is transmitted to line during operation of relay DA.

Referring to the graphical diagram it will be seen that for the first portion of the Z pulse period a train of rhythmic pulses is producedat a pair of contacts PA, while during the remainder of the period another train of rhythmic pulses,

Assuming both relays MMA and MMB are operated thereby indicating that three further.

registrations are required on meter M'I'R, then when relay DA operates two different and successive rhythmic signal trains are sent over the line to the satellite DSR to produce this effect in the following manner.- Relay DA in operating at armature da3 replaces the full earth connection to the winding of the battery feeding and impulsing relay AM by a rectifier earth confilters out the higher frequency harmonic comi ponents of the original rectangular wave-shape D. C. pulses so as only to allow the passage to line of the fundamental low frequency component which will not interfere with any conversation which may be taking place over the line.

.- The PA rhythmic train is received atthe DSR on the responding movements RA and RB but only movement RA which is tuned to this particular rhythm will satisfactorily respond and after a short build up period the movement will gather sufficient swing to operate its contacts m, and so will bring up relay MA. Relay MA in operating locks independently of contacts ra and at armature maZ brings up relay SA, whereupon positive battery is extended over armatures ma l, sa3 and bl on to the incoming private lead P So as to effect a second registration of the meter MTR. Relay.

SA in operating disconnects the locking circuit for relay MA at its armature sat. and the metering pulse therefore persists for the slow releasing time of relay MA, relay SA remaining held via armatures mb3, saL'sbl and 132 to earth. At conclusion of the PA rhythmic train the PB train follow and after a further build-up period movement RB responds and closes its contacts rb to bring up relay MB which locks. Relay MB in operating disconnects the holding circuit for relay SA at armature 111133, and after the slow releas period of this relay, relay MA is re-operated by the earth extending forward over armatures b2, sbl, saZ and mb5. 'On operation of relay MA; relay SA is re-operated and this relay again disconnects the circuit to relay MA at its armature saZ. During the subsequent release time of relay MA relay SB is brought up over a circuit from earth, armatures b2, sa2, sal, mb3' and ma3.

and locks, while another pulse is delivered over armatures ma l, $113 and bl to the meter MTR which thus receives its third registration. On release of relay MA the holding circuit for relay SA is opened at armature mat since its alternative locking circuit is opened at operated armature mb? and on release of relay SA the circuit to relay MB through armature sa2 is disconnected since the alternative locking circuit for this relay is disconnected at the'operated arma ture sbl. During the release time-of relay MB thefourth registration is effected on the meter MTR over armatures sbZ, mb l, sa3 and bl and on release of this relay relay SB remains held over armatures 3b! and 112 to prevent further operation of the metering relays even if further pulses should be received from the sending end. The case has thus been described where four I unit fees are registered against the calling party,

the first .of which is transmitted by battery reversal in the normal manner and the next three of which are transmited over the conversational path by rhythmic signals as "described. In case. only two unit fees are required "a PA trainxof rhythmic signals only will be transmitted after the ordinary battery reversal metering signal and relay MA willibe aloneoperated to give the additional pulse, relay MB not being operated in this case, while if thre unit fees are required a PE rhythmic signal will be transmitted when relays MB and MA will be operated in quick succession and two additional pulses will be generated as will be readily understood from the previous description where relay MA is not operated originally but only after MB.

In regard to the operation of the responding movements RA and RB it will be seen that in the example being described a steady current flow from the battery feeding relay AM persists throughout the signal transmission cycle. This steady current will be arranged to bias the movements in the direction to which they will be operated by the signal'pulses and it is not thought that any undue difficulty will arise dueto this cause; Alternatively it could be arranged that the steady current and superimposed signal currents are received on a thermionic device which is triggered into operation on each signal pulse and which extends operating pulses of constant value to the responding movements regardless of the value of the input currents. The circuit of the thermionic device will be arranged so that it will only trigger into operation when a signal pulse is received.

Responding movements of the type described possess a high degree of sensitivity and a very small amount of signalling energy is therefore required to produce operation thereof, so that very weak signals may be employed thereby fur-- ther tending to prevent interference with conversation on the path'over which the signals are extended,

Although in the example described use has been made of smoothed direct current signals it will be appreciated that these signals could also be of alternating current at the required low frequency. The responding relays may be operated through transformers and half-wave dry contact rectification arrangements might be interposed in circuit therewith at the receiving end in order that operating pulses at the required rhythm may be delivered to said movements.

Cadence responding movements are particularly insensitive to signals other than those to which they are tuned to respond, since for any one cadence movement a number of operating pulses at the correct predetermined rhythm must be received before operation can take place. With certain types of movement it may be possible for aparticularly strong surge voltage produced in the speaking path to operate the responding device and to prevent false operation from this cause, use might be made, as described in the application previously referred to, of units of non-linear resistance material which will be bridged across the input leads to the operating coils of the responding movements and which will ensure that the power input to these coils never exceeds a-certain limiting value irrespective of the strength of signal received.- Such nonlinear resistance material will preferably be of the silicon-carbide type. The use of thermionic valve trigger arrangements at the receiving point will also overcome the above-mentioned trouble.

One circuit difliculty arises in connection with the signalling scheme described, in that if the calling party should flick his'receiver hook during signal transmission, then the signalling pathwill be broken at armature all of the satellite DSR impulsing relay A and some of the pulses of a signal may be lost. .This trouble is overcome by arranging that-if the signalling cycle should be interrupted then it will be subsequently 'recommenced and repetition thereof will continue repeatedly until a complete unbroken cycle can be transmitted to the receiving point, arrangements being made at-thereceiving end to avoid duplication of metering by repeated signalling cycles.

It will be seen from Fig, 4 that during the sig-' nal transmisis'on relays DA and DB are held operated in series from the battery potential supplied to the common Z lead, while relay DB is also held operated over its lower winding. If'the calling party should. flick his receiver hook during the Z pulse period, then relay AM in releasing will release relay DMand will bring up relay CM which opens'.the circuitsof the relays DA and DB, whereupornsince the line supervision relay DM will subsequently 're-operate, relayDA will be reconnected to. the 8 lead and the signalling cycle will recommence on receipt of the next S pulse. If the subscriber should flick his switch hook during the reception of an S pulse when relay DA is held operated therefrom, relay DA will release momentarily during the release of relay DM but it may ire-operate to the S pulse with I the re-operation of relay DM and the signal cycle will subsequently commence in normal manner, but if the switch hook should be flicked after elapse of the S pulse and before commencement of the Z pulse, during whichtime relay DA is held operated. over its middle winding, then this relay will be restored by relay CM and sending out of the signal transmission will be deferred until after relay DA hasre-operated on the subsequent S pulse. If relay CM should be operated after the transmission of a complete metering cycle, relay DB will remain operated over its armature dbl, resting armature dal and armature bml and the operation of relay GM will therefore be without effect.

Referring now to the signal receiving point at Fig. 3, if during reception of a PA signal train in the normal manner to effect metering. Similar remarks apply in connection with a PB signal cycle and a combined PA and PB signalling cycle, the arrangements always being such that if a received signal has become effective at the receiving point prior to the interruption of the signal cycle, then if such a cycle is repeated it cannot have any cumulative effect at the receiving point. Furthermore, if a signal has not become effective at the receiving point, then the subsequent repetition of the signal train will cause the desired metering to take effect in normal manner. If both frequencies of pulses are being transmitted and one is effective and the other is interrupted, the repetition of the pulses will only have effect as regards the one which is interrupted. I

It will be appreciated that it is not necessary, in the case of multi-fee (level 8) calls originated by main exchange subscribers, for metering pulses to be extended over the conversational path as described, since use can be made of the P wire which will be available for signalling'in this instance and over which ordinary positive battery metering pulses can beextended in normal manner.

From the foregoing description it will be seen that the invention provides a ready and efficient means of signalling over a conversational path during conversation, the use of differing rhythm frequencies enabling a plurality of signal discriminations to be effected without introducing complex circuit arrangements.

I What we claim as new and desire to secure by Letters Patent is:

1. In atelephone system, a speech transmission path, means for establishing connections of differentvalue over said path, means for impressing upon said path a Wave of a particular frequency outside of the audio frequency band, when a connection of one value is established, means for impressing upon said path a wave of another frequency outside of the audio frequency to register a charge for the second connection.

2. In a telephone system, means for establishing a speech transmission path having a direct current flowing therein, a relay having a movable element mechanically tuned to a certain frequency outside of the audio-frequency range and having an operating coil linked to said speech transmission path, and means effective during the transmission of speech over said path to impress upon said path spaced apart electrical impulses comprising unidirectional undulations in,

the current flow thereover and occurring at said certain frequency, thereby to cause said relay coil to operate said element in synchronism with said impulses.

3. In a telephone system, an audio frequency circuit, means for impressing impulses of unidirectional current of different sub-audio frequencies upon said circuit at different times, means associated with said circuit for discriminating between the impulses of different subaudio frequencies impressed uponsaid circuit, said last means including a plurality of pendulums having. different periods of vibration and means for operating each pendulum responsive only to the receipt of unidirectional impulses, a sub-audio frequency coinciding with the frequency of that. pendulum,

4. In a telephone system, a speech transmisrent from said second source, whereby said second source, upon each operation of said means, cooperates with said first source to increase the gized variably in accordance with the variations in the flow of current over said path, said relay also having a mechanically tuned element whose vibratory period coincides in length with the length of said intervals, whereby said relay coil causes said element to vibrate in synchronism with the operations of said means.

5. In a multi-metering telephone system, a speech transmission path, a rectifier, a source of direct current connected to said path via said rectifier, said rectifier being 'so poled as to per mit the current from said source to flow over said path, a second source of direct current, means for at times bridging said second source across said rectifier in such a direction thatsaid rectifier is not conductive to current from said second source; whereby said second source cooperates with said first source to increase the tablishing' connections "of" difierent value over said path, means operated after a connection has been completed over said path for transmitting pulses of unidirectional current over said path of a frequency or rhythm differing in accordance with the value of .the'connection, and means responsive to said pulses to assess different charges for the connection, said pulses being below audible range and of such form as to have no efiect on speech transmission over said path.

7. In a telephone system, a, speech transmispulses at another rate over said path when connections are extended to another point, a pair of devices connected to said path each responsive to impulses of only one of said rates, a meter, and means controlled by each device to operate the meter a different number of times.

REGINALD TAYLOR. GEORGE THOMAS BAKER.- 

